Activated carbons are used in various applications for adsorption because of their increased specific surface areas and developed pore structures. In order to effectively exhibit functions in such applications, there is an increasing demand for activated carbons that have appropriate physical properties. It is known that physical properties such as adsorption performance of activated carbons are influenced by the structure of the activated carbons and mainly by the specific surface area of the activated carbons. However, since activated carbons are hydrophobic and have low performance in adsorption of polar substances (substances having polar groups) such as water, it has been difficult to apply the activated carbons in applications for adsorption of moisture (water vapor) in air such as an adsorbent for an adsorption heat pump using water vapor as an operation medium. In addition, since activated carbons have poor wettability to water and the contact of activated carbons with water is insufficient, the activated carbons have low adsorption capacity to substances to be adsorbed in water. Consequently, the efficiency of adsorption of substances to be adsorbed in water (liquid) has been low as compared with the case where the activated carbons were used in air (gas).
In recent years, technologies for enhancing the hydrophilicity of activated carbons have been studied through various researches, and activated carbons in which a water vapor adsorption amount can be increased have been proposed, whereas the water vapor adsorption amount has been insufficient in the conventional activated carbons.
For example, in Non-Patent Document 1, a technology for enhancing the hydrophilicity by subjecting activated carbons to oxidation treatment with an oxidizing agent such as hydrochloric acid, nitric acid and the like to impart acidic functional groups to the surface of the activated carbons has been proposed.
Furthermore, in Non-Patent Document 2, a technology for enhancing the hydrophilicity by adding urea or melamine to resorcinol-formaldehyde resin to incorporate nitrogen in the carbon skeleton (ring structure) of the activated carbons has been proposed.